Note: Descriptions are shown in the official language in which they were submitted.
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DEVICE FOR DETECTING POSITION
FIELD OF THE INVENTION
The invention relates to an apparatus for detecting the
position of an object which can move along a predefined path. Such
apparatus may be used for controlling the position of a lift cage or the like
and thus ensuring its positioning at predetermined stops according to floor
levels.
BACKGROUND OF THE INVENTION
European patent 0 694 792 discloses an apparatus of this
type for detecting the position of a moveable object, which has an acoustic
signal waveguide which extends along a travel path and has a
predetermined, uniform speed of propagation of sound, and a signal input
coupler, which is connected to a signal generator and is located on the
moveable object, to couple an acoustic signal into the acoustic signal
waveguide. In this case, signal output couplers are arranged at both ends
of the acoustic signal waveguide and are each connected to a counter, the
two counters being clocked by a clock generator and connected to a
subtracter for the output signals from the two counters. The output signal
from the subtracter, as a measure of the propagation-time difference of the
acoustic signal coupled in from the point at which it is coupled in to the
signal output couplers, can be processed by an evaluation unit to form a
signal which is representative of the instantaneous position of the
moveable object on the travel path, the signal input coupler operating with
a signal spacing which is greater than the propagation time of sound from
one end of the travel path to the other. In the case of very long travel
paths,
such as occur, for example, in lifts in multi-storey buildings, the lifts
often
also being operated at high speed, the distance resolution which can be
achieved is inadequate, however.
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SUMMARY OF THE INVENTION
It is an object of the invention to provide an apparatus for
detecting the position of an object which can move along a predefined
path, with which it is possible to monitor, simply and accurately, the
position of the moveable object on a travel path of great length.
An apparatus for detecting the position of an object moveable
along a predetermined travel path in accordance with the present invention
comprises
an acoustic signal waveguide extending along the travel path and
having a predetermined, uniform speed of propagation of sound;
a signal input coupler located on the moveable object, to couple a
clocked acoustic signal into the acoustic signal waveguide,
at least one signal output coupler being arranged at one end of the
acoustic signal waveguide and being connected to an evaluation unit for
determining the propagation-time of the sound signal from a position at
which it is coupled in to the at least one signal output coupler and for
generating a signal that is representative of the instantaneous position of
the moveable object on the travel path,
wherein the signal input coupler couples in, as acoustic signal,
synchronization pulses with a clock period which is greater than the time of
propagation of sound from one end of the travel path to the other, and a
large number of additional pulses inbetween.
Further objects, embodiments and advantages of the
invention will become apparent from the following description and the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in more detail below with
reference to a preferred embodiment illustrated schematically in the
appended drawings.
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Fig. 1 shows an apparatus for detecting position in schematic
form in accordance with the invention.
Fig. 2 shows a timing diagram relating to the signals from the
apparatus of Fig. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The illustrated apparatus for detecting position, which can be
used in particular for detecting the position of a lift cage, comprises an
acoustic signal waveguide 1, for example a steel rail or especially a
metallic wire, which extends along a predefined travel path, along which a
moveable object 2, for example a lift cage, can move to and fro. The
acoustic signal waveguide 1, having a predetermined, uniform speed of
propagation of sound, is clamped or held in a damped manner at both ends
in a damping clamping means or holder 3.
The moveable object 2 carries a signal input coupler 4, which
is connected to a signal generator 5, for example an oscillator, via a signal
matching circuit 4'. The signal input coupler 4, which, in particular,
operates
inductively, couples an acoustic signal which periodically includes a
synchronization pulse S received from the signal generator 5, into the
acoustic signal waveguide 1. The synchronization pulses S have a clock
period greater than the duration of the propagation of the acoustic signal
from one end of the acoustic signal waveguide 1 to the other.
In addition, the signal input coupler 4 couples in additional
pulses M, specifically a large number of additional pulses M during each
clock period of the synchronization pulses S. The clock period of the
additional pulses M is such that a distance resolution, needed for example
for braking and for moving to an exact position of the object 2, is achieved
in the direction of the travel path.
The synchronization pulses S are marked, that is to say can
be distinguished from the additional pulses M during the evaluation. The
marking can be made, for example, by their clock period being an
appropriate multiple of the clock period of the additional pulses M, and
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additionally by their offset in time in relation to the additional pulses M,
for
example by one half clock period, cf. the pulse train generated by the
signal generator 5 in the first line of Fig. 2. Then, a predetermined number
of additional pulses M in each case follows a synchronization pulse S.
However, the marking can also be made in any other way,
thus the synchronization pulses S can be distinguished from the additional
pulses M by modulation, pulse width, pulse height or the like.
The synchronization and additional pulses S, M to be coupled
in may be short electromagnetic pulses, for example simple pulses or pulse
trains, or a periodic frequency shift.
A signal output coupler 6 is in each case arranged at the ends
of the acoustic signal waveguide 1. This is preferably a piezoelectric signal
output coupler 6, but those operating inductively or capacitively can also be
used.
Each signal output coupler 6 is connected to a signal
matching circuit 7, whose output lines in each case lead to a counter 8.
Both counters 8 are clocked by a clock generator 9, an oscillator. The clock
period of the clock generator 9 is considerably lower than the propagation
time of the sound from one end of the acoustic signal waveguide 1 to the
other and is selected in accordance with the desired measurement-path
resolution. The outputs from the counters 8 are fed to a subtracter 10,
which forms the difference between the output signals from the counters 8
and feeds them to an evaluation unit 11, for example a microprocessor,
where the output signal from the subtracter 10 is evaluated.
The synchronization pulses S are used to indicate to the
evaluation unit 11 which following pairs of additional pulses belong to each
other, namely the respective nth, that is to say first, second, third and so
on, additional pulses M arriving at the two signal output couplers 6
(designated by A and B in Fig. 2) at different times Ta and Tb following the
respective synchronization pulse S, in order that the evaluation unit 11 can
detect or determine the associated absolute time difference Ta - Tb = OT
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between associated additional pulses M, and hence the position of the
object 2.
The evaluation in order to detect the position is primarily
carried out in relation to the additional signals M, however the
synchronization pulses S can also be evaluated in this regard, specifically
above all, but not exclusively, when the respective mth additional pulse is
specially marked, in order in this way to serve as a synchronization pulse
S.
If the moveable object 2 is located at the centre between the
signal output couplers 6, the outputs from the counters 8 are equal and
their difference is zero. If the object 2 (in the case of a vertical path) is
above the centre, the output from the counter 8 connected to the upper
signal output coupler 6 is smaller than that from the other. The
propagation-time difference determined by the subtracter 10 between the
mutually associated additional pulses M in the acoustic signal waveguide 1,
and the known speed of sound in the latter, gives the distance of the
moveable object 2 from the centre. Since, if the moveable object 2 were to
be located below the centre, the difference would have a different sign, it is
also known whether the moveable object 2 is located above or below the
centre, that is to say the precise position of the moveable object 2 can
therefore be calculated. A digital or analogue position signal produced in
this way by the evaluation unit 11 can be used for subsequent control.
A watchdog 12 (monitor circuit) in the evaluation unit 11 can
be used for the simple monitoring of the measurement path, given
time-invariant input coupling of the signal coupled in. In the event of
contamination which is capable of damping the signal on the acoustic
signal waveguide 1, the difference determined by the subtracter 10
exceeds a predetermined value, to which the watchdog 12 responds in
order to trigger an appropriate warning signal or the like.
The speed of sound in an acoustic signal waveguide 1 made
of steel is about 5300 m/s. Given a time resolution of 188 ns, for which
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purpose a clock generator frequency of 5.3 MHz is necessary, the
positional resolution of the measurement path is 1 mm.
Instead of being coupled to the signal generator 5, the signal
input coupler 4 may be triggered by evaluation unit 11 to couple the
acoustic signals into the signal waveguide 1. Instead it is also possible that
the signal input coupler 4 triggers the evaluation unit 11 via an electric
signal to define the temporal start of each coupling of an acoustic signal
into the signal waveguide 1 for the evaluation to be done by the evaluation
unit 11.
Instead of the preferred provision of a signal output coupler 6
at each of the two ends of the signal waveguide 1, only one signal output
coupler 6 provided at one of the ends of the signal waveguide 1 may be
used.
While the invention has been shown and described with
reference to a preferred embodiment, it should be apparent to one of
ordinary skill in the art that many changes and modifications may be made
without departing from the spirit and scope of the invention as defined in
the claims.
